, new research suggests.
Oromandibular dystonia causes an involuntary opening of the mouth, which can be disabling and disfiguring. Although injection of the lateral pterygoid muscle with botulinum toxin is the preferred treatment for oromandibular dystonia, a potential complication concerns the maxillary artery, which can run either lateral or medial to the lateral pterygoid muscle.
In a study of 200 Turkish patients, researchers documented significant variations between men and women in the anatomical location of the maxillary artery – and even found lateral versus medial differences on the left and right side in the same individual.
“The results showed that the maxillary artery runs lateral to the muscle in 67% of the Turkish patients,” Rezzak Yilmaz, MD, department of neurology, University of Ankara Medical School, Turkey, reported at the International Congress of Parkinson’s Disease and Movement Disorders.
Given this high rate, there is a high risk for injury “that may result in pain and hematoma” when using preauricular extraoral injections, Dr. Yilmaz and colleagues noted. Instead, they recommend an intraoral injection approach to the lateral pterygoid muscle. “However, this critical anatomical variation is still unrecognized by most clinicians performing [botulinum toxin] injections,” they wrote.
Significant gender differences
The maxillary artery is the largest branch of the external carotid artery.
In the current study, the researchers used magnetic resonance angiography to assess the relevant anatomy in a cohort of 200 individuals (mean age, 56.4 years; 64% women) without a history of facial trauma or movement disorders.
Results showed that the maxillary artery ran lateral to the lateral pterygoid muscle in 67% of the study population.
“This result was also more frequent in females compared with males. Also, there was a considerable variability between the left and the right side in 20% of the participants,” Dr. Yilmaz reported.
Statistically significant gender differences were found for the artery running lateral to the lateral pterygoid muscle on both sides (71.1% in women vs. 58.5% in men; P = .007) and for the artery running lateral to the lateral pterygoid muscle on just the left side (69.8% in women vs. 53.5% in men; P = .02).
In an email exchange, Dr. Yilmaz said if medical personnel are not trained to perform an intraoral approach, “imaging to visualize the path of the maxillary artery before an extraoral/transcutaneous injection can be recommended.”
“If the imaging reveals that the maxillary artery passes lateral to the muscle, then the patient needs to be referred to another center for an intraoral injection,” unless the clinician is trained for an intraoral approach, he added.
Useful education
Commenting on the study, Michele Tagliati, MD, director of the Movement Disorders Program at Cedars-Sinai Medical Center, Los Angeles, said the results were educational. “I didn’t know about all this variability. I was working under the assumption that the artery was medial,” said Dr. Tagliati, who was not involved with the research.
Among his large practice of about 2,000 patients, Dr. Tagliati estimated having five patients for whom he provides this type of injection – and has never encountered a problem with them.
“Maybe all my patients are medial, but now that I’m aware I’ll probably pay more attention,” Dr. Tagliati said. He does not currently perform magnetic resonance angiography before injecting them, “although maybe I should,” he said.
When asked if it is worth the time and expense to perform magnetic resonance angiography on every patient who comes in for lateral pterygoid muscle injections, Dr. Tagliati said that although he has done the injections without problems in his current patients, he may “start obtaining imaging studies to make sure that we’re not taking unnecessary risk” if the maxillary artery is lateral to the lateral pterygoid muscle in new patients.
If there is a risk, he’ll then consider talking with colleagues in oral or facial surgery. Dr. Tagliati added that the number of patients he sees with oromandibular dystonia is rather small, so this extra step would not add a lot of additional imaging.
Overall, Dr. Tagliati noted that the study outcome was significant enough to want to use it for professional education. “I can definitely tell you that I’m going to bring it to the attention of my Fellows. [Every year] I teach one or two Fellows to inject Botox,” he said.
There was no funding for the study. Dr. Yilmaz and Dr. Tagliati have disclosed no relevant financial relationships.
A version of this article first appeared on Medscape.com.